The invention relates to a method for forming a socket on a pipe of biaxially oriented polyvinyl chloride.
Such a method is disclosed by NL-A-9400894. The pipe of biaxially oriented polyvinyl chloride may, for example, have been fabricated by means of the methods as described in WO 95/25627, WO 95/25628 and WO 95/30533.
In the case of the method disclosed by NL-A-9400894, and end section of the pipe on which the socket is to be formed, is slipped onto a support section of a mandrel, which support section fits into the pipe. Then the internally supported pipe end section is heated, whereupon a socket-forming mandrel section which adjoins the support section and whose shape substantially corresponds to the intended shape of the socket is formed into the heated end section of the pipe. Finally, the pipe end section still supported by the mandrel is cooled.
It was found that in the case of pipes on which sockets had been formed by means of the known method, cracking occurred in a large number of cases in the socket section of the pipes. These cracks sometimes occurred even while the sockets were being formed, but also if the sockets were subsequently subjected to an impact load.